photopatch test

pho·to·patch test 'fōt-ō-.pach- n a test of the capability of a particular substance to photosensitize a particular human skin in which the substance is applied to the skin under a patch and the area is irradiated with ultraviolet light

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a type of patch test for assessing the photosensitization potential of medications and other chemicals. On the patient's back, each substance is applied in two different locations; then one spot of each substance is irradiated. A positive reaction at only the irradiated site of a substance indicates photoallergy; reaction at both the irradiated and the nonirradiated sites indicates a different type of allergic reaction.